A polyimide film has been extensively used in the fields of electric/electronic devices, semiconductors and so on, because of its excellent heat resistance, chemical resistance, mechanical strength, electric properties, dimensional stability and so on. For example, for a flexible printed circuit board (FPC), there has been used a copper-clad laminated substrate where a copper foil is laminated on one or both sides of a polyimide film.
In general, a polyimide film may not provide a laminate having adequately high peeling strength when a metal layer is formed on a polyimide film by dry plating such as metal deposition and sputtering, or when a metal layer is formed on a polyimide film by wet plating such as electroless plating.
Many of polyimides, particularly many of high heat resistant polyimides mainly containing an aromatic group is insoluble in organic solvents. Therefore, a high heat resistant polyimide is produced by a method including forming a self-supporting film (may be referred to as a gel film) using a polyimide precursor solution such as polyamic acid which is not fully polyimidized, and heating it to complete imidization. Although soluble polyimides are also known, the soluble polyimides known to date are generally low heat resistant, and components of a polyimide having relatively high heat resistance is limited.
Patent Document 1 has described a polyimide prepared by using a triazine-based diamine, showing an example in which a polyimide solution is applied on a metal foil. In addition, as examples of the use of a triazine-based diamine, Patent Document 2 has disclosed an end-modified imide oligomer prepared by using a triazine-based diamine, and Patent Document 3 has disclosed a polymer electrolyte prepared by using a triazine-based diamine. Patent Document 4 discloses a polyimide which is prepared by using a triazine-based diamine having two amino groups (—NH2) in para-positions in benzene rings relative to two NH groups bonded to the triazine rings (hereinafter, it may be referred as “p-ATDA”). Further, Patent Document 5 has disclosed that a laminate of a polyimide film prepared by using a triazine-based diamine and a metal foil has excellent adhesiveness and adherence.